Core, Unit and Z0T

[Simon Peyton-Jones]

| Are Unit and Z0T considered equal?

No, the are not.  Z0T is the zero-tuple type ()
Unit is used only in generic programming, and can be written "1" (in
types)>

| In GHC/Base.hcr they are both defined:
| 
| -----
|    %data GHCziBase.Unit =
|      {GHCziBase.Unit};
|    %data GHCziBase.Z0T =
|      {GHCziBase.Z0T};

That's right

| In .../ghc/compiler/prelude/primops.txt at line 2669 we find:
| 
| -----
| primop  FinalizeWeakOp "finalizeWeak#" GenPrimOp
|     Weak# a -> State# RealWorld -> (# State# RealWorld, Int#,
|                (State# RealWorld -> (# State# RealWorld, Unit #)) #)

OK, this is where the wierdness is.  The "Unit" here should probably be
"()".  When
processed into Haskell to give the type of finalizeWeak#, the Unit
becomes unitTy,
and that in turn is defined in prelude/TysWiredIn to be the zero-tuple
type ().

So primops.txt is very misleading here.  I'll fix it to use () instead.

Simon